The present invention generally relates to a composition and an associated method for inhibiting stain formation on a ferrous metal surface. The present invention particularly relates to a composition and an associated method for inhibiting stain formation on a ferrous metal surface after acid pickling of the ferrous metal surface.
The process utilized to manufacture steel results in an oxide layer or xe2x80x9cscalexe2x80x9d being formed on the surface of the steel. Typically, the scale is removed from the surface of the steel by a process commonly known in the industry as pickling. Pickling generally includes advancing the steel through a series of aqueous baths (e.g. four baths) containing hot (85xc2x0 C.) hydrochloric acid and ferrous chloride. After the above described acidic treatment, the acid and salt (i.e. ferrous chloride) deposited on the steel must be removed. Removing the acid and salt typically includes advancing the steel through a number of rinsing baths where the surface of the steel is sprayed, flooded, or immersed in hard, softened, or demineralized water.
While the above described process effectively removes the scale, acid, and salt from the steel, it suffers from a number of drawbacks. In particular, removing the scale with the acidic treatment generates a xe2x80x9cchemically reactive fresh surfacexe2x80x9d on the steel which can react with substances present in the rinse bath environment. For example, if the advancement of the steel through the rinsing baths is stopped so that the steel remains in the rinse bath environment for a relatively extended period of time (e.g. 1 to 5 minutes) chemicals such as oxygen, residual acid, and/or salts present in the rinse bath environment react with the surface of the steel. The reaction of these substances with the surface of the steel results in a stain and/or a rust spot being formed on the surface. Unfortunately, the advancement of the steel through the rinsing baths is periodically stopped for relatively extended periods of time due to power outages, mechanical breakdowns, or the time required to weld pieces of steel together prior to undergoing the pickling process. Therefore, the section of steel positioned within the rinse baths during these periodic stops will have a number of stains or rust spots formed thereon. Before the steel can be used to fabricate other products, such as cars, the stains and/or rust spots must be removed by repickling the steel or by cutting out the stained and/or rusted sections. Neither method is desirable since both increase the cost of manufacturing steel.
Therefore, in light of the above discussion, it is apparent that what is needed is a composition and an associated method which substantially inhibits or prevents the formation of stains and/or rust spots on a steel surface during the aforementioned rinsing process.
In accordance with one embodiment of the present invention, there is provided an effective passivating composition for adding to an aqueous rinse which is applied to a ferrous metal surface after treatment of the ferrous metal surface with an aqueous acid solution. The composition includes a salt of gluconic acid and a polyquaternium compound.
Pursuant to another embodiment of the present invention, there is provided an effective passivating composition for inhibiting stain formation on a ferrous metal surface. The composition includes a base. The base is present in the composition in an amount sufficient to adjust the pH of an aqueous rinse to a value greater than 7.0 after the composition is added to the aqueous rinse. The composition also includes a gluconate and Poly[oxy-1,2-ethanediyl(dimethyliminio)-1,3-propanediyliminocarbonylimino-1,3-propanedily (dimethyliminio)-1,2-ethanediyl dichloride]. Poly[oxy-1,2-ethanediyl(dimethyliminio)-1,3-propanediyliminocarbonylimino-1,3-propanediyl (dimethyliminio)-1,2-ethanediyl dichloride] is present in the composition in a sufficient amount such that after the composition is added to the aqueous rinse Poly[oxy-1,2-ethanediyl(dimethyliminio)-1,3-propanediyliminocarbonylimino-1,3-propanediyl (dimethyliminio)-1,2-ethanediyl dichloride] is about 0.003% to about 0.05% by weight per liter of the aqueous rinse.
Pursuant to yet another embodiment of the present invention there is provided a method of inhibiting stain formation on a ferrous metal surface. The method includes the step of contacting the ferrous metal surface with (i) a salt of gluconic acid and (ii) a polyquaternium compound.
It is therefore an object of the present invention to provide a new and useful composition and associated method for inhibiting stain and/or rust formation on a ferrous metal surface after treatment with an aqueous acid solution.
It is another object of the present invention to provide an improved composition and associated method for inhibiting stain and/or rust formation on a ferrous metal surface after treatment with an aqueous acid solution.
The above and other objects, features, and advantages of the present invention will become apparent from the following description and attached drawings.